熔體混溶與T6熱處理對多元過共晶Al-18%Si合金組織和性能的影響
發(fā)布時間：2018-10-04 18:37
【摘要】：鑒于合金凝固行為、組織和性能顯著地受其熔體狀態(tài)的影響,以及我們過去的研究表明,采用經(jīng)歷熔體結(jié)構(gòu)轉(zhuǎn)變的高溫熔體,與半固態(tài)的低溫熔體混溶,能使二元鋁硅合金中的初晶硅顯著細化。本文在優(yōu)化原混溶工藝的基礎(chǔ)上,以多元過共晶鋁硅合金(Al-18Si-1.5Cu-0.5Mg-0.5Mn-0.2Ti)為研究對象,系統(tǒng)研究了熔體混溶與Sr變質(zhì)復(fù)合處理、T6熱處理對合金組織形態(tài)和性能的影響,同時深入分析了諸種工藝的作用規(guī)律和機制。從挖掘材料潛能和工程實際應(yīng)用的角度,為工業(yè)生產(chǎn)提供了工藝技術(shù)和基本原理方面的參考依據(jù)。主要結(jié)論如下:(1)常規(guī)鑄造下,初晶硅多呈板塊狀和八面體形態(tài),具有典型的小平面生長特征。合金經(jīng)高低溫熔體混溶與Sr變質(zhì)復(fù)合處理后,初晶硅顯著細化(晶粒尺寸細至10.27μm),且棱角鈍化,表現(xiàn)出非小平面特征,共晶硅同時轉(zhuǎn)變?yōu)樯汉鳡睢?2)對于高低溫熔體混溶能夠顯著細化初晶硅,作者分析,主要得益于三方面:一,高溫熔體熱沖擊半固態(tài)低溫熔體,分解、產(chǎn)生了大量初晶硅的同質(zhì)形核核心;二,熔體經(jīng)歷結(jié)構(gòu)轉(zhuǎn)變后,凝固形核過冷度增加,形核率顯著增加;三,熔體經(jīng)歷結(jié)構(gòu)轉(zhuǎn)變后,系統(tǒng)自由能降低,硅晶體生長障礙增大,抑制了初晶硅的長大。而初晶硅棱角的鈍化,主要是由于經(jīng)歷熔體結(jié)構(gòu)轉(zhuǎn)變的高溫熔體促使了硅晶體生長界面發(fā)生了動力學(xué)粗糙化,從而使其生長界面由小平面向非小平面轉(zhuǎn)變。(3)固溶處理過程中,共晶硅形貌發(fā)生了明顯的改變,并顯著影響著合金性能。固溶初期,共晶硅發(fā)生熔斷和鈍化,合金硬度得到提高;固溶中期,共晶硅球化且粒度適中,合金硬度達到峰值;固溶后期,共晶硅明顯粗化,合金軟化。(4)時效研究表明,隨著時效溫度的提高,合金硬化速率顯著加快,但硬化能力不同,175℃時效處理時獲得最佳硬度峰值。此外,在175℃和195℃下,時效曲線出現(xiàn)“雙峰”現(xiàn)象,并結(jié)合脫溶DSC曲線,認為單、雙峰現(xiàn)象與時效過程的序列析出有關(guān),而GP區(qū)向亞穩(wěn)相轉(zhuǎn)變有明顯時間間隔是產(chǎn)生雙峰曲線的主要原因。最終確定合金最佳T6熱處理工藝為:520℃固溶8h,175℃時效8h。(5)力學(xué)性能測試表明,合金經(jīng)混溶處理后,布氏硬度、抗拉強度及延伸率分別提高11.0-14.0%、15.9-19.8%、55.7-58.9%,磨損量降低8.8-12.1%,分析認為主要與硅顆粒細化所產(chǎn)生的細晶強化,及硅顆粒固有斷裂抗力的提高有關(guān)。而經(jīng)T6熱處理后,布氏硬度、抗拉強度分別提高32.4-36.0%、39.9-44.7%,磨損量降低21.6-25.4%,認為主要與沉淀相彌散析出所引起合金強度的提高有關(guān)。
[Abstract]:In view of the solidification behavior of the alloy, the microstructure and properties are significantly affected by its melt state, and our previous studies have shown that high temperature melts that undergo structural transformation of melts are mixed with semi-solid cryogenic melts. The primary silicon in binary Al-Si alloy can be refined obviously. Based on the optimization of the original miscibility process, the effects of melt miscibility and Sr modification on the microstructure and properties of multicomponent hypereutectic Al-Si alloy (Al-18Si-1.5Cu-0.5Mg-0.5Mn-0.2Ti) were studied systematically. At the same time, the action law and mechanism of various kinds of processes are analyzed in depth. From the point of view of excavating the potential of materials and practical application of engineering, this paper provides a reference for industrial production in terms of process technology and basic principle. The main conclusions are as follows: (1) under conventional casting, primary silicon is mostly plate-shaped and octahedral, with typical small plane growth characteristics. After high and low temperature melt miscibility and Sr modification, the primary silicon is refined (grain size up to 10.27 渭 m), and angular passivation), showing non-small plane characteristics. At the same time, eutectic silicon is transformed into coralline. (2) for high and low temperature melt miscibility, primary silicon can be significantly refined. The author analyses that the main benefits are as follows: first, high temperature melt heat shock semi-solid low temperature melt, decompose, decompose, A large number of homogenous nucleation cores of primary silicon were produced; second, the supercooling degree of solidification nucleation increased and the nucleation rate increased significantly after the melt experienced structural transformation; third, after the melt experienced structural transformation, the free energy of the system decreased and the growth barrier of silicon crystal increased. The growth of primary silicon was inhibited. The passivation of the prism angle of primary silicon is mainly due to the high temperature melt undergoing melt structure transformation, which results in the dynamic coarsening of the growth interface of silicon crystal, which makes the growth interface of silicon crystal change from Xiaoping to non-small plane. (3) in the process of solution treatment, The morphology of eutectic silicon has changed obviously and the properties of the alloy have been greatly affected. In the early stage of solution, eutectic silicon was melted and passivated, and the hardness of eutectic silicon was improved. In the middle stage of solution, eutectic silicon spheroidized and its particle size was moderate, and the hardness of eutectic silicon reached its peak. At the later stage of solution, eutectic silicon became coarser and alloy softened. (4) Aging study showed that, With the increase of aging temperature, the hardening rate of the alloy accelerates significantly, but the best hardness peak value is obtained when the hardening ability is different at 175 鈩，
本文編號：2251449
[Abstract]:In view of the solidification behavior of the alloy, the microstructure and properties are significantly affected by its melt state, and our previous studies have shown that high temperature melts that undergo structural transformation of melts are mixed with semi-solid cryogenic melts. The primary silicon in binary Al-Si alloy can be refined obviously. Based on the optimization of the original miscibility process, the effects of melt miscibility and Sr modification on the microstructure and properties of multicomponent hypereutectic Al-Si alloy (Al-18Si-1.5Cu-0.5Mg-0.5Mn-0.2Ti) were studied systematically. At the same time, the action law and mechanism of various kinds of processes are analyzed in depth. From the point of view of excavating the potential of materials and practical application of engineering, this paper provides a reference for industrial production in terms of process technology and basic principle. The main conclusions are as follows: (1) under conventional casting, primary silicon is mostly plate-shaped and octahedral, with typical small plane growth characteristics. After high and low temperature melt miscibility and Sr modification, the primary silicon is refined (grain size up to 10.27 渭 m), and angular passivation), showing non-small plane characteristics. At the same time, eutectic silicon is transformed into coralline. (2) for high and low temperature melt miscibility, primary silicon can be significantly refined. The author analyses that the main benefits are as follows: first, high temperature melt heat shock semi-solid low temperature melt, decompose, decompose, A large number of homogenous nucleation cores of primary silicon were produced; second, the supercooling degree of solidification nucleation increased and the nucleation rate increased significantly after the melt experienced structural transformation; third, after the melt experienced structural transformation, the free energy of the system decreased and the growth barrier of silicon crystal increased. The growth of primary silicon was inhibited. The passivation of the prism angle of primary silicon is mainly due to the high temperature melt undergoing melt structure transformation, which results in the dynamic coarsening of the growth interface of silicon crystal, which makes the growth interface of silicon crystal change from Xiaoping to non-small plane. (3) in the process of solution treatment, The morphology of eutectic silicon has changed obviously and the properties of the alloy have been greatly affected. In the early stage of solution, eutectic silicon was melted and passivated, and the hardness of eutectic silicon was improved. In the middle stage of solution, eutectic silicon spheroidized and its particle size was moderate, and the hardness of eutectic silicon reached its peak. At the later stage of solution, eutectic silicon became coarser and alloy softened. (4) Aging study showed that, With the increase of aging temperature, the hardening rate of the alloy accelerates significantly, but the best hardness peak value is obtained when the hardening ability is different at 175 鈩，
本文編號：2251449
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